Get Ready for Comet PanSTARRS!

Hi All,

I've been reading the discussions on this forum about comet imaging. The following thread has lots of useful information to consider.

http://forums.dpreview.com/forums/post/50650544

It's now time to be firming up plans on how to capture some images of Comet PanSTARRS. Not only is the performance of the comet an uncertainty, but also each of us will be subject to the weather at our location during the critical period of best visibility - March 8-20. For mid-northern observers, March 12-17 will be a particularly good time.

We are getting reports strongly suggesting that the comet may be less spectacular than hoped. That doesn't lesson the opportunity it presents to hone our skills and research what will enable getting some nice results. Our experience here will likely be of great use later in the year for Comet ISON.

There are a number of sources of information on the comet's current and predicted performance. One you might look at is Sky and Telescope magazine's coverage in its February and March issues. You'll find some of that information in the following link:

http://www.skyandtelescope.com/skytel/beyondthepage/Comet-PanSTARRS-Updates-185665152.html

The timing and circumstances of best visibility will of course vary depending where you live on Earth. But since it will be brightest around the time of its close approach to the Sun and Earth, we will be dealing with an object that sets soon after the Sun. It will be low in the twilight sky, presenting a challenge from the light pollution standpoint. As the sky darkens, the comet will be sinking lower and getting dimmer. Yet that may be an opportunity as well, since the twilight sky colors can be quite striking. A less-than-bright comet low in the sunset will present some challenges in getting the exposure right as well as in tracking. There's also a good opportunity for including a very thin crescent Moon near the comet on the nights of March 12th and 13th. For the best viewing (in the mid northern latitudes) we will need a site with a good view to the West and Northwest, with as little light pollution as possible in that direction. We don't want to add to the twilight glow.

We should be getting more reports on brightness of the nucleus and length of tail. It would be useful to have a good idea of the angular coverage of whatever lenses we have to use. For those who may not know how to figure this, I'll give an example using my camera. It's a simple formula using just one constant:

• 57.3° = 360°÷(2 X pi)
  

This number is also known as a ​Radian​. The formula may not always be exact. But it will get you pretty close in most cases, particularly in the longer focal lengths. Here it is:

Angular coverage = (Sensor dimension) ÷ (Lens focal length) X 57.3°

My Sony NEX-5N sensor has dimensions of 15.6mm X 23.4mm.

For that sensor with a 55mm lens, this works out to be

(15.6mm) ÷ (55mm) X 57.3° = 16.3° and

(23.4mm) ÷ (55mm) X 57.3° = 24.4°

So my APS-C sensor with a 55mm lens will cover about 16.3° by 24.4°. "Crop factor" has no bearing on the result. All that matters is sensor size and lens focal length.

I hope what I've presented here will be of some use. What other advice do any of you have for us? Lets hope for an interesting comet and good weather for our imaging.

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Best Regards,
Russ